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The Sun was thought to have little activity in its new cycle that began a year ago.

But new predictions point to very intense solar activity that would peak in July 2025.

Spots and sun activity

The Sun is a gigantic ball of boiling gas subjected to an intense magnetic field.

In places on the solar surface with the greatest magnetic activity, large dark spots that can reach the size of our planet are formed.

Sunspots appear, grow, change in appearance, decrease in size and disappear, on average, after about two weeks.

They usually appear in pairs, each spot presenting the opposite polarity, thus forming the poles of a gigantic magnet whose magnetic intensity can be ten times greater than that of the Earth's magnetic field.

Sunspot number (known as Wolf number) is a measure of the activity of our star.

This number varies periodically, following a cycle of approximately 11 years.

At the beginning of a cycle, the solar surface is clear of spots (solar minimum), little by little spots begin to appear at high solar latitudes which, then, multiply and spread towards the equatorial regions, until the maximum is reached solar.

Magnetic cycles

This apparent 11-year cycle is actually half of the Sun's total magnetic cycle (or Hale cycle) lasting 22 years.

And it is that, over 11 years, the orientation of the solar magnetic field gradually changes and causes it to reverse between the northern and southern hemispheres.

After a complete cycle of 22 years, the orientation of the solar magnetic field is again the same as at the beginning.

There are direct measurements of the number of sunspots since the 17th century.

And, in addition, this number has been able to be inferred by indirect methods (for example, by measuring the rings of tree trunks) to the last 11,000 years, thus forming one of the most complete databases in the history of astronomy.

Studying the evolution of sunspots is extremely important because their number is associated with solar flares.

When the cycle of the spots reaches its maximum, the Sun is at its highest activity, and that is when the largest solar storms are triggered that, if they are directed towards Earth, can damage the high-tech systems on which we depend so much. .

Sunspots in previous cycles and predicted for cycle 25S.

McIntosh / RB

The sun has already awakened

During the year 2019 we went through a particularly calm period of solar minimum, the Sun did not have a single spot for 274 days.

Thus the so-called 'Solar Cycle 24' was closed.

And with the arrival of the first spots at high latitudes, in December of that same year, we entered Cycle 25. The Sun is already awake.

During 2020, the average number of sunspots was 7.8 per day, but in the last months of the year, the average number of sunspots exceeded 30.

Several international groups of experts have been studying the behavior of the Sun during the last years to make predictions of the activity during this Cycle 25. All these groups reached similar conclusions: the maximum should be reached in July 2025 with a total of 115 spots.

This prediction was very similar to the data from Cycle 24 which, in turn, was the cycle with the least activity in the last 100 years.

New prediction

However, a new work coordinated by Scott McIntosh (NCAR, USA), after analyzing sunspot data from the last 270 years, arrives at a radically different prediction.

According to this team, the weakness of Cycle 24, augurs that the new cycle will be particularly active.

The number of spots predicted for July 2025 would exceed 200, that is, practically double that of 115 previously estimated.

This new study is based on a different extrapolation method.

McIntosh is based on the behavior of the blob bands as they move from high latitudes towards the equator and on the 'termination' event that occurs at that final moment.

According to the researcher, observing the times between completions in each cycle, throughout the 270 years studied, it can be deduced what the next cycle will be like.

Specifically, the shorter the time between terminations, the more intense the next solar cycle appears to be.

However, the McIntosh model does not have the consensus of solar physicists.

The validity of the method can only be verified over the next few months, because if the activity is going to be so intense, it should begin to manifest itself right away.

In fact, the existing data to date indicate that the number of sunspots in this Cycle 25 is 80% higher than the equivalent period of Cycle 24, but these data refer to a relatively short time interval.

It is still too early to validate the new predictions.

The debate sparked by this work illustrates the difficulties of predicting solar activity.

There are many different methods to carry out these extrapolations, some based simply on the recent behavior of the spots and others based on models that try to simulate the physical phenomena of the Sun.

The latter, which seem to be more reliable today, need to know the value of the magnetic field at the solar poles.

And, according to some researchers, the polar magnetic field would determine the solar activity of the next cycle.

This value is very difficult to measure at present, but the European Solar Orbiter probe (in which Spain plays an important role [https://bit.ly/39gbHMQ]) should provide images of the solar poles in 2025, during the maximum, which could greatly contribute to refining the activity prediction models.

Vulnerable technology

The activity of our society, both on land and in space, has become highly dependent on delicate technological systems and, therefore, very vulnerable to solar storms.

Particles from solar flares, when ejected in the direction of our planet, can damage communications systems, electrical distribution networks, and many other technological equipment.

In order to carry out planning work in electrical and aerospace companies, the continuous monitoring of the Sun and the development of reliable forecasting methods is therefore of vital importance.

McIntosh and colleagues have published their results in the journal

Solar Physics.

The manuscript of his article entitled "Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude" can be consulted here.

Rafael Bachiller is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.

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